1. Field of Invention
The present invention relates to apparatuses, storage media, and methods for using various data, such as audio data and video data, using computer systems, and more specifically, relates to a data management apparatus which can use data advantageously in terms of data capacity, a storage medium having stored therein a data management program, a storage medium having stored therein usage certificate data, and a method of using data.
2. Description of Related Art
A delivery service has been offered on a network, such as the Internet or the like, in which audio data of music performed by a famous artist or video data for a movie can be downloaded to a user's terminal under the condition that a user pays a predetermined fee.
The delivery service is implemented by a seller's WWW (World Wide Web) server. The seller's WWW server stores many pieces of audio data and the like. When a user accesses the WWW server for the first time, the user is required to input name, address, credit card number, and the like, and hence the user is registered. At the same time, the seller's WWW server issues an ID and password to the user. The user uses the issued ID and password to access the seller's WWW server, and downloads desired audio data or the like to the user's terminal. When the seller's WWW server is accessed by the user, the seller's WWW server authenticates the user based on the ID and password input by the user. When audio data or the like is downloaded, the seller's WWW server refers to the credit card number specified by the ID input by the user, and deducts a predetermined charge from a user's account.
In recent years, it has been possible to use various data, including audio data and the like, by using portable terminals, such as cellular phones and the like. For example, i-mode offered by NTT Communications Network, Inc. (NTT DoCoMo) leads in this field.
When the user uses the above delivery service to access audio data or the like by a portable terminal, the user generally stores the data in the portable terminal for a while and enjoys playing the data several times, since the user has paid a charge to purchase the data. Also, the user may want to store not only a single piece of audio data but also several pieces of audio data in the portable terminal and to enjoy various data.
When using audio data or the like with the portable terminal, the number of pieces of data that can be stored in the portable terminal is limited, since it is difficult to install a large-capacity memory in the portable terminal due to issues of cost reduction and size. Specifically, audio data or the like is much larger than document data, such as text data or the like. In fact, it may be impossible to store a single piece of audio data that requires a few hours to be played.